Starting circuits for electrical space discharge tubes



M. BAREISS A ril 27, 1937.

STARTING CIRCUITS FOR ELECTRICAL SPACE DISCHARGE TUBES Filed Nov. 26, 1934 27 LOAD j INVENTOR MAX BAREISS v BY ATTORNEY Patented Apr. 27, 1937 UNITED STATES PATENT OFFICE STARTING CIRCUITS FOR ELECTRICAL SPACE DISCHARGE TUBES Application November 26, 1934, Serial No. 754,730

6 Claims.

This invention relates tostarting circuits for electrical space discharge tubes, and more particularly to such circuits for gaseous discharge rectifiers using a separately-heated, thermionic cathode. 1 1

An object of this invention is to produce a system which impresses an elevated voltage between the cathode and an anode of such a tube for starting, which voltage drops to the normal vvalue when the discharge is initiated.

Another object is to provide a novel time delay circuit for such a system.

A still further object is todevise an arrangement in accordance with the preceding objects, which is simple in construction, positive in action, and effective in operation.

The foregoing and other objects of my invention will be best understood from the following exemplification thereof, reference being had to the drawing wherein the single figure is a diagram of the. circuit arrangements of one form of my novelsystem. 7

In space discharge tubes, particularly of the gaseous discharge type, a voltage sufiicient to initiate a discharge through the tube is usually considerably greater than the Voltage which is necessary to maintain a discharge after it has once started. Therefore, in many systems in which the supply voltage is relatively low, it is advisable. to provide special arrangements whereby starting of a discharge through the tube is insured. In-variousfsystems the load is intermittent and thus the starting arrangement should be available and operative each time the load is disconnected to insure a restarting of the discharge-when the. load is again connected to the system. Suchja system may be the arc welding arrangement as shown in the copending application of Crout, Serial No. 742,913, filed September 6, 1934. My present invention may be used in such an arrangement, and effectively provides a suitable starting system therefor. Of course it is to be understood that my invention may likewise be, useful in a wide variety of other arrangements.

In the drawing, I represents a gaseous dis.- charge rectifier of any suitable type, such as that, for example, shown in the copending application of Spencer and Marshall, Serial No. 729,101, filed June 5, 1934. The rectifier l comprises a cathode 2 heated by a separate heating filament 3, and having a plurality of anodes 4. In the arrangement as shown, I have illustrated the rectifier l as, having six such anodes. The rectifier contains a suitable gaseous atmosphere, such as, for

example, mercury vapor. The anodes 4 are energizedfrom a transformer 5 having three primary windings 6, and 8 and six secondary windings 9, l0, ll, l2, l3 and I4. One end of each of the six secondary windings is connected to a central neutral point l5. The outer ends of the six secondary windings are connected to the six anodes 4, respectively. The three primary coils 6, and 8 are connected preferably in a delta connection, the three corners of which are connected through three reactor coils I6, I! and |8 to the three line conductors I9, and 2|, respectively, of a threephase A. C. source. A control switch 22 may be. interposed in order to connect or disconnect the transformer 5 from the line conductors I9, 20 and 2|, respectively. The reactors l6, I1 and I8 are simultaneously adjustable in order to control the output of the rectifier I, as more fully described in said copending Crout application. The heating filament 3 may be energized from a fila ment transformer 23 having a primary winding 24, connected to two of the line conductors l9 and 20 and a secondary winding 25 connected to the ends of the heating filament 3. A conductor 26 passes from the cathode 2 to one output terminal 26 while a conductor 21 pases from the neutral point l5 to the other output terminal 21. Any suitable load may be connected between the terminals 26' and 21'. A shunt 28 across which an ammeter 29 is connected may be provided in order to enable the current in the load circuit to be read. A voltmeter 30 may likewise be connected between the two load conductors 26 and 21 in order that the voltage across the load may be read.

In order to provide an excess voltage for starting purposes, I provide a starting circuit by connecting one of the anodes, for example the anode connected to secondary winding through a conductor 3|, a control thermostat 32, a resistance 33, a conductor 36, and conductor 26 to the cathode 2. Across the secondary winding 25 is also bridged a heating coil for the thermostat 32. An indicating lamp 36 is connected across the resistance 33.

In some devices of this kind it may be desirable to have the cathode at temperature of thermionic emission before any load is connected to the system. In this case, when the control switch is first closed, the load circuit is kept open. Upon closure of said switch 22, the filament transformer 23 energizes the heating filament 3, which starts to raise the temperature of the cathode 2. It is also sometimes desirable to prevent the starting of a discharge through the rectifier until the cathode has been raised to temperature of thermionic emission. If the starting circuit is put in operation before the cathode has reached the proper temperature, a discharge may be initiated which might localize on some undesirable spot of the cathode system. Therefore, the thermostat 32 is provided which in its cold position opens the starting circuit. When, however, the filament transformer 23 starts to supply the heating fila ment 3 with current, it likewise energizes the heating coil 35. This heating coil 35 raises the temperature of the thermostat 32, and causes it to move from its cold position to its hot position, wherein said thermostat 32 closes the starting circuit. The constants of the system are so chosen that the thermostat 32 does not close the starting circuit until the cathode has reached a safe operating temperature. Upon the starting circuit being closed, the anode 4 connected to the secondary coil II is connected directly to the cathode by the circuit traced above.

In many cases the time delay afforded by the thermostat 32 may be eliminated and the starting circuit may be permanently connected from the anode 4, connected to the winding I I, through the resistance 33 to the cathode. The operation of this starting circuit is as follows. Before the discharge is initiated in the rectifier I, no current flows through the starting circuit, and therefore there is no drop through the resistance 33 therein. Thus the anode connected to the secondary coil I I is at the same potential as the cathode 2. The voltage induced in the secondary coils II and I4 is in such a direction that the total voltage between the outer ends of the coils I I and I4 is substantially double the voltage across either one of these coils. Before a discharge starts, therefore, the anode 4 connected to the secondary coil I4 has impressed between it and the cathode 2, double the voltage appearing across any one of the secondary coils. This likewise is double the maximum voltage which would be impressed between any one of the anodes and the cathode in absence of the starting circuit. This excess voltage is sufficient to insure the starting of an ionizing discharge between the cathode 2 and the anode 4 connected to the secondary coil I4. As soon as an ionizing discharge occurs, current flows through the starting circuit, and therefore through the resistance 33. This current produces a voltage drop through the resistance 33 which raises the potential of the anode 4 connected to the secondary coil I I above that of the cathode 2, and tends to return the potential of the oathode 2 to that of the neutral point I5. Under these conditions the potential distribution throughout the system is restored to normal operating condition. The load may then be connected into the load circuit. If the load is subsequently disconnected and for some reason the discharge through the tube stops, the current through resistance 33 stops, and thus the excess voltage is reapplied to the tube to insure restarting of the tube.

The indicating lamp 3B which is connected across the resistance 33 gives to the operator a visual indication of the starting of the tube. When a current flows through the resistance 33 upon the starting of the rectifier tube l, the voltage which appears across the resistance 33 is sufficient to light the lamp 33. When the operator sees that the lamp 35 is lit, this indicates to him that the system is ready to have the load connected thereto. The lamp 36 is not essential to the operation of the device, and where simplification is desired, this lamp may be omitted.

Of course it is to be understood that this invention is not limited to the particular details of the arrangement as described above as many equivalents will suggest themselves to those skilled in the art. For example, instead of furnishing an operator with a visual indication as to when the load is to be connected to the system, the visual indicator might be replaced by a relay which would close the load circuit at the proper time. Also instead of having six anodes, such as illustrated, the space discharge tube might have any number of anodes, provided that number is greater than one. The invention can likewise be applied to space discharge tubes other than those utilizing thermionic cathodes, said invention being useful in any space discharge tube in which the starting voltage is greater than the normal operating voltage. Various other changes and uses in and for the various novel parts of my system will readily suggest themselves. It is accordingly desired that the appended claims be given a broad interpretation commensurate with the scope of the invention within the art.

- What is claimed is:

1. In combination, a gaseous discharge device comprising a cathode and a plurality of anodes, an energizing transformer for said discharge device having a winding with its ends connected to two of said anodes, an external circuit connected between the cathode and a point intermediate the ends of said winding, a continuously conductive starting circuit connecting one of said anodes tosaid cathode to maintain said anode and cathode at substantially the same potential before starting, and means in said starting circuit for producing a potential difference between said cathode and anode connected thereto upon the passage of a current through said starting circuit.

2. In combination, a gaseous discharge device comprising a cathode and a plurality of anodes, an energizing transformer for said discharge device having a winding with its ends connected to two of said anodes, an external circuit connected between the cathode and a point intermediate the ends of said winding, a continuously conductive starting circuit connecting one of said anodes to said cathode to maintain said anode and cathode at substantially the same potential before starting, and a resistance in said starting circuit.

3. In combination, a gaseous discharge rectifier comprising a cathode and a plurality of anodes, an energizing transformer for said rectifier having a winding with its ends connected to two of said anodes, a load circuit connected between the cathode and a point intermediate the ends of said winding, a continuously conductive starting circuit connecting one of said anodes to said cathode to maintain said anode and cathode at substantially the same potential before starting, and means in said starting circuit for producing a potential difference between said cathode and anode connected thereto upon the passage of a current through said starting circuit.

4. In combination, a gaseous discharge device comprising a cathode, a plurality of anodes, an energizing transformer for said discharge device having a winding with its ends connected to two of said anodes, an external circuit connected between the cathode and a point intermediate the ends of said winding, a starting circuit connecting one of said anodes to said cathode, heating means for heating said cathode to temperature of operation, a switch in said starting circuit, means for closing said switch after said heating means has been energized for a predetermined length of time, and means in said starting circuit for producing a potential difierence between said cathode and anode connected thereto upon the passage of a current through said starting circuit.

5. In combination, a gaseous discharge device comprising a cathode, a plurality of anodes, an energizing transformer for said discharge device having a winding with its ends connected to two of said anodes, an external circuit connected between the cathode and a point intermediate the ends of said winding, a starting circuit connecting one of said anodes to said cathode, heating means for heating said cathode to temperature of operation, a switch in said starting circuit, a thermostat 15 for closing said switch in its hot position, means adapted to be energized simultaneously with said heating means for heating said thermostat, and means in said starting circuit for producing a potential diflerence between said cathode and anode connected thereto upon the passage of a current through said startingcircuit.

6. In combination, a gaseous discharge device comprising a cathode and a plurality of anodes, an energizing transformer for said discharge device having a winding with its ends connected to two of said anodes, an external circuit connected between the cathode and a point intermediate the ends of said winding, means for establishing the potential of said cathode substantially the same as the potential of one of said anodes before starting, and means responsive to the starting of a discharge for establishing a substantially normal difference of potential between said cathode and said last-named anode.

MAX BAREISS. 

